During the next year we shall begin experiments designed to 1) determine which of the histone subtypes of S. purpuratus embryos are present in nucleosomes; 2) isolate each subtype in pure form; 3) determine the chemical nature of the differences between them by peptide mapping and sequence analysis; 4) prepare subtype-specific immune sera; 5) study locations of the subtypes in the embryo of immunofluorescence.